When you remove a TDB-dataset over HTTP from the Fuseki server, Fuseki does not close the file.
Steps to reproduce:
First: create a dataset over HTTP with name 'x'. Then, delete the dataset with name 'x'. Now inspect the open files of the fuseki process by running lsof -p <FUSEKI_PROCESS_ID> you see that a dataset with name 'x' is still opened by the Fuseki-process.
When a Fuseki process runs for a long time, and many datasets are created and deleted, it will in the end lead to a situation in which you cannot create new datasets anymore. Each attempt to creating a dataset will lead to a HTTP response code 500 with message 'java.nio.file.FileSystemException: /var/lib/fuseki/templates/config-tdb: Too many open files'. Also, keeping the files open leads (I suspect) to a higher memory usage than strictly needed.